Patent GB-1064522-A (GB)
Title: Controllable semi-conductor rectifiers
IPC: H01L23/482
Filed: 1964-08-04
Abstract: 1,064,522. Semi-conductor controlled rectifiers. SIEMENS-SCHUCKERTWERKE. A.G. Aug. 4, 1964 [Aug. 3, 1963; March 25, 1964], No. 31466/64. Heading H1K. In a PNPN controlled rectifier the control electrode contacting one of the inner layers lies in an aperture in the adjacent outer layer, this aperture having an elongate parallel-sided slit-like portion. The uncompensated charge carrier concentration at the surface contacted by the control electrode is at least 10<SP>16</SP> and the preferred range is 8À10<SP>17</SP> to 5À10<SP>18</SP> cm.<SP>-3</SP>. Fig. 2 shows the basic structure, comprising an initially N crystal of silicon which has been diffusively doped with one or more of the dopants aluminium, gallium and boron to form an outer P region which-by milling, etching or sandblasting- is separated with two layers 3, 4 either by removing the edges of the crystal to expose the inner N zone or, as shown, by merely forming an annular groove breaking into the N region. Gold-antimony and gold-boron foils are alloyed to provide respectively the rectifying electrode 5 and the ohmic electrodes 7 and 10. In the latter case aluminium may be used instead of gold-boron. The resulting structure has a substantially annular N-region 6 underlying the electrode 5, and the electrode 7 lies in the centre of this annulus. The annulus is broken by at least one elongate aperture or slit: as shown in Fig. 1 there are two slits so that electrode 5 and region 6 are both in two parts 5a, 5b and 6a, 6b but Figs. 4 to 6 (not shown) depict similar forms with, respectively, four, six and one slits. Fig. 7 (not shown) depicts the rectifier of Figs. 1 and 2 housed in a sealed enclosure, the base of which is a copper heat sink (11). Alloyed to this base, e.g. by the surface roughening technique described in Specification 1,007,186, is a molybdenum or tungsten carrier plate (17) between which and the base (11) there may be a thin silver layer. The rectifier (16) is alloyed to the carrier plate (17). The other terminal electrode is connected to the copper head (15) of the enclosure via a molybdenum annulus (20), copper annulus (19), steel annulus (21) and copper tube (18). The control electrode is contacted by a copper pin (28) attached to a silver lead-out wire (34). Insulators (13, 22, 31, 32, and 35) isolate the three electrode systems. Fig. 9 (not shown) depicts an alternative form of the Fig. 1 rectifier in which a pair of aligned slits extend in opposite directions from a central circular aperture, but these slits may terminate short of the periphery of the outer electrode layer so that this layer is not divided into two halves as it is in Fig. 1. Fig. 8 (not shown) depicts an appropriate modification to the mount of Fig. 7 for accommodating the Fig. 9 rectifier. Fig. 12 (not shown) depicts a rectifier in which the aperture for the control electrode (63) is a simple slit. The control electrode lead-out is a silver or gold strip (65) which, in the mounting of Fig. 13 (not shown) will be clamped between steel or Fe-Ni-Co annular discs (72, 73). These discs are spaced by insulators from the terminal electrodes (70, 71) which are of a ductile precious metal such as silver.